The present invention relates to printing devices and, more particularly, to devices in which recording is accomplished by means of an ink jet printer.
Ink jet printers, such as shown in U.S. Pat. No. 3,701,998, issued Oct. 31, 1972, to Mathis, have gained increasing popularity, due in part to the ease with which such printers may be interfaced with electronic data processing equipment. In an ink jet printer, one or more orifices receive an electrically conductive recording fluid, such as for instance a water base ink, from a pressurized fluid supply manifold and eject the ink in one or more parallel jet drop streams. These recorders accomplish graphic reproduction by selectively charging and deflecting the drops in each of the streams and, thereafter, depositing at least some of the drops on a sheet or web of copy paper or other print material. Charging of the drops is accomplished by application of control signals to charging electrodes positioned near each of the streams. As each drop breaks off from its parent fluid filament, it carries with it a charge which is, in effect, a sample of the voltage present on the associated charge electrode at the instant of charge separation. Thereafter, the drop passes through an electrostatic field and is deflected in the field direction by a distance which is proportional to the magnitude of the drop charge. Various printers have been developed in which the drops are charged binarily for print or no print operation. Other printer systems selectively charge drops to various print potentials and deflect the drops from each jet to a number of print positions.
It will be appreciated that the resolution of the final print image is a function of the size of the ink drops and the inter-drop spacing on the print material. The spacing between the jets on a print head is limited by the size of the charge electrode structures adjacent associated jets and the deflection electrodes. The spacing between jets, in turn, is a factor which must be taken into account in design of a system to insure that sufficient image resolution is provided.
A number of approaches have been taken to insure sufficient resolution of the print image. As disclosed in the above cited Mathis patent, multiple rows of jets may be positioned in tandem with each row servicing print lines on the print medium which interlace with the print lines serviced by other rows of jets. In another approach, jets may be spaced apart by substantial distances and the print medium repeatedly scanned. After a sufficient number of scans, each jet will have serviced a number of print lines on the print medium forming a band of a width equal to the inter-jet spacing. Such an arrangement is shown in a drum copier environment in U.S. Pat. No. 3,689,693, issued Sept. 5, 1972, to Cahill et al, and assigned to the assignee of the present invention.
Another approach taken is disclosed in U.S. Pat. No. 4,009,332, issued Feb. 22, 1977, to Van Hook. In Van Hook, one or more more jet arrays are moved axially along a rotating drum upon which a sheet of copy paper is mounted. In a single array embodiment, comprising n nozzles spaced k resolution elements apart print lines along the axis of the drum, and the nozzle array is advanced axially with respect to the drum by n resolution elements during each revolution of the drum. The numbers k and n are chosen such that they have no prime factors in common greater than unity. Rotation of the drum and movement of the jet array in this system are continuous and result in a plurality of interlaced print lines which are slightly inclined with respect to the copy paper. IBM Technical Disclosure Bulletin Volume 15, Number 11, dated May 1976, at page 3917 discloses a similar interlace scheme in which the jet nozzle array is positioned circumferentially around the print drum.
The above interlace schemes are not readily adaptable to a computer print out device in which successive lines of print information are provided by a computer to a line printer device in the sequence in which they are to be printed since these schemes require the assembly of a complete page of image information prior to printing. U.S. Pat. No. 3,871,004, issued Mar. 11, 1975, to Rittberg, discloses a print arrangement for printing lines of image information across an intermittently moving print web. After each movement of the print web, the print head is moved across the web and a number of print lines are imaged. In the Rittberg device, resolution is increased by providing deflection electrodes which deflect the drops from each jet to a number of print lines. Extensive reorganization of the print data is required before it can be supplied to the print head.
Accordingly, there is a need for a non-contacting printing device in which printing may be accomplished with good resolution across an intermittently moving print medium and in which sufficient inter-jet distance may be maintained without undue reordering of print information.